This invention relates to an acceleration responsive switch which closes contacts in response to positive or negative acceleration occurred in the case of crash of an automobile or the like, so that a protection system such as air bag system for a driver or passengers may be operated.
Various types of the above-described acceleration responsive switches have been proposed. For example, one of them comprises a spherical inertial member serving as a solid pendulum for closing switch contacts. Another type employs combination of a pressure sensor and an electronic circuit. Further another type comprises a hermetically sealed glass receptacle containing mercury.
The electronic circuitry employed in prior acceleration responsive switches may fail under the influence of a pulsed high voltage due to discharge of static electricity induced during the driving of an automobile or an abnormal high current and high voltage induced in the case of a thunderbolt. Thus, the prior art switches employing the combination of the pressure sensor and electronic circuit have a reliability problem. In the case of the acceleration responsive switch of the type wherein the contacts are operated through a link mechanism by the solid inertial member, a long time use of the switch causes the contact fault and malfunction of the link mechanism. These faults cannot be found with ease and, accordingly, the switch has a problem that it is likely not to be energized when necessary. Further, the switch including an air-tightly sealed glass receptacle containing mercury has a problem of variations in operating characteristics. Additionally, since the glass receptacle is likely to be damaged, it is difficult to handle the switch. Moreover, even when the glass receptacle has a minute crack, it cannot be found at the beginning of use. A long time use of the switch enlarges the crack, which causes leakage of the charged gas and mercury.